Thousands of people in Laos, whose homes were swept away when a dam burst, are sheltering in areas contaminated by landmines, humanitarians said, as floods and mud hamper aid delivery.

The United Nations said this week that 34 people were reported dead, 97 were missing and 6,000 had been evacuated due to flash floods that followed the collapse of a hydropower dam in Laos last month.

Attapeu Province in southern Laos is “highly contaminated” by unexploded ordnance, it said, with almost 320 hectares (791 acres) in Sanamxay district, where people are sheltering in camps, “confirmed hazardous areas”.

“There’s a real danger that explosive items on or in the ground will have moved,” said Blossum Gilmour, country director for Mines Advisory Group (MAG), a British charity that works to clear unexploded ordnance, said.

“Areas which have been cleared of bombs may need re-clearing … But also, as people are evacuated from their homes, they may be relocated to places which have not yet been cleared.”

Laos is the most heavily bombed country per capita in the world as a result of bombing by the United States when it was waging war in neighbouring Vietnam in the decade up to 1973, according to MAG.

Much of the Southeast Asian nation is still contaminated by landmines, despite decades of clearance efforts, with about 300 new casualties each year, many of them children, it says.

Laos was hit by a tropical storm on July 18 and 19, which caused flooding in parts of 13 provinces, including Attapeu, the UN said.

As floodwaters rose, a saddle dam that was part of Laos’ US$1.2 billion Xe-Pian Xe-Namnoy hydropower project collapsed, sending torrents of water crashing into neighbouring villages.

The UN said three camps “remain largely inaccessible” and that aid officials were in discussion with the military about using its helicopters to provide “last mile delivery” of relief items, including food.

With seasonal rains continuing until September and water levels rising in the Mekong River and its tributaries, “flooding across the country may spread further,” the UN said.